Enhanced Sensitivity of Wired and Wireless Measurement for Liquid Concentration Based on a Modified Cylindrical Cavity

This article presents a miniaturized microwave sensor based on a cylindrical cavity for detecting the concentration of water-glucose solutions. To enhance the sensitivity, the cavity is modified in which two symmetrical metal wires with respect to its center are embedded. Compared with the conventional cavity, in the wired measurement, the modified sensor has increased sensitivities by 53% and 44% in terms of shifts of reflection and transmission resonant frequencies
${f}_{{11}}$
and
${f}_{{21}}$
, which are 17.86 and 14.16 MHz/1% concentration, respectively. In addition, semiwireless and passive full-wireless measurement methods are proposed. With a measuring distance of 30 cm, experimental results show that the sensitivities of the semiwireless measurement are 8.82 and 6.11 MHz/1% for
${f}_{{11}}$
and
${f}_{{21}}$
, which are increased by 50% and 35%, respectively, compared with the conventional cavity. The proposed full-wireless measurement with advantages including passivity, long-distance, and low-cost has a high sensitivity of 2.74 MHz/1% with the reading distance of 30 cm. Compared with other microwave glucose sensors, the proposed sensor has a better performance and the wireless methods are novel, which are expected to be used in biological and chemical sensors.